The objective of this study is to define functions involved in nonhomologous site specific recombination, a process involved in the integration into the bacterial genome of a number of different genetic elements; temperate phages such as lambda, transposable antibiotic resistance elements, and insertion sequences (IS). Toward this end we have developed techniques for enriching and screening for Escherichia coli host mutants (him) in which integration of phage lambda is restricted. A number of these mutants have already been isolated and partially analyzed. We proposed to continue the isolation and characterization of such mutants in the following ways: (1) All mutations will be mapped. (2) The effect of the mutations on site-specific recombination of lambda will be quantitatively assayed. (3) The effect of the mutations on transposition of various transposable genetic elements will be stuided. (4) The nature of a mutation in phage which overcomes the effect of the him mutations will be studied.